Flexible risers are commonly used in subsea oil and gas production installations to connect floating production, storage and offload (FPSO) facilities with seabed oil and/or gas flowlines. The end of the flexible riser at the FPSO is connected to the FPSO piping system. A bend stiffener is provided around the end of the riser at the connection to the FPSO. The main role of the bend stiffener is to absorb bending moment applied to the pipe by the movement of the FPSO and wave action on the riser. Without a bend stiffener the riser will overbend, which will result in early failure of the riser. The area of the bend stiffener corresponds to a high loading zone for the flexible riser and is known as being critical in terms of fatigue of the riser. The main fatigue mechanism of the riser is due to bending. An assessment of the fatigue applied to the riser is critical to estimating its remaining life time.
A device for controlling stiffeners of flexible pipes is described in WO 2006/003308 which uses optical fibres containing fibre Bragg gratings which are embedded within a bend stiffener to monitor the curvature/bending of the pipe within the bend stiffener region. This device suffers from the problem that it can only be used for new pipeline installations since bend stiffeners are installed for the lifetime of an installation and are not designed for replacement.